Extruding metal members of varying wall thickness



Jan. 9, 1968 A. M. MURPHY ETAL 3,362,203

EXTRUDING METAL MEMSERS OF VARYING WALL THICKNESS Filed Jan. 7, 1965 7 Sheets-Sheet 1 INVENTORQ LFRED MICHAEL MURPHY LJNWOOD E. HOWELL \AALTEF? F. MUTTER Jan. 9, 1968 A. M. MURPHY ETAL 3,362,208 v I EXTRUDING METAL MEMBERS OF VARYING WALL THICKNESS Filed Jan. 7, 1965 7 Sheets-Sheet 2 ATTORNEYS Filed Jan. 7, 1965 Jan. 9, 1968 f r A RPH ETAL 3,362,208

EXTRUDING METAL MEMBERS OF VARYING WALL THICKNESS 7 Sheets-Sheet 5 ilw @L N 9\ AL mvsmons ALFRED MICHA L 5 MURPEIY LINWOODEHOWELL M Q WALTER F. MU'I'TER Jan. 9, 1968 A. M. MURPHY ETAL 3,362,208

EXTRUD ING METAL MEMBERS OF VARYING WALL THICKNESS Filed Jan. 7, 1965 7 Sheets-Sheet 4 Jill \ 1* L- INVENTORfi f v v ALFRED MICHAEL 9Q MURPHY u NWOOD EHOWELL WALTER F MUTTER {ATTORNEYS Jan. 9, 1968 A. M. MURPHY ETAL 3,362,208

EXTRUDING METAL MEMBERS OF- VARYING WALL THICKNESS Filed Jan. 7, 1965 7 Sheets-Sheet 5 (I I" r 1 g INVENTORS ALFRED MICHAEL *M RPHY UNWOOD E. I -IOW Ll. WALTER F. MUTT Q'ZZMQAM M ATTORNEYS 7 Sheets-Sheet 6 QQN NN A. M. MURPHY ETAL EXTRUDING METAL MEMBERS OF VARYING WALL THICKNESS Filed Jan. '7, 1965 Jan. 9, 1968 ATTORNEYS Jan. 9, 1968 A. M. MURPHY ETAL 3,362,208

EXTRUDING METAL MEMBERS 0F VARYING WALL-THICKNESS File dJan. '7, 1965 7 Sheets-Sheet 7 IIUF 1 INVENTORS ALFRED MICHAELMLRPHY Ll NW H OOD E OWELL WAL R F. MUTTER XZM, @409 4:72am

ATTQRNEYS United States Patent 3,362,208 EXTRUDING METAL MEMBERS OF VARYIN WALL THICKNESS Alfred Michael Murphy and Linwood E. Howell, Chester, and Walter F. Mutter, Richmond, Va., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed Jan. 7, 1965, Ser. No. 424,106 6 Claims. (Cl. 72-260) ABSTRACT OF THE DISCLOSURE A metal extrusion press mandrel with a tapered or stepped tip is hydraulically advanced and retracted during extrusion, thereby changing the Width of the extrusion orifice and extruding tubing whose wall thickness varies along its longitudinal axis.

This invention relates to methods and apparatus for extruding elongate members. More particularly, this invention relates to methods of extruding metal tubes of varying wall thickness and apparatus for carrying out such methods.

Metal tubes of varying wall thickness have many varied uses. A number of such uses require that the tube have difierent strengths along its length. As a general principle, use of a tube of constant wall thickness sufiicient to meet the most severe of such strength requirements results in a tube having an excess of material in the remaining portions of tube, which excess unnecessarily adds to the cost and weight of the tube. For example, a tube section is often desired to be joined to another tube or member at some location or locations along its length, and greater strengths are usually required at such joints than at the remainder of the tube. A specific example occurs where several tube sections are joined at their ends to form a continuous pipe, as discussed in the copending and co-assigned US. application Ser. No. 809,190, now Patent No. 3,176,494. These heavy end tube sections are made thicker at their ends, where they are joined to one another. It must be noted, however, that tube sections may be desired to be joined at locations other than their ends, either to other tube sections or to other members, such as supporting members, and that such locations can occur uniformly or non-uniformly along the length of the tube section, in accordance with a particular design. An alternative example of the above-mentioned general principle occurs where the strength requirements vary along the length of the tube either uniformly or non-uniformly as a function of the magnitudes, direction, and location of loads placed upon the tube. A specific example occurs where a tube is supported at one end only and there is a bending moment on the tube or the weight of the tube itself constitutes a substantial portion of the load.

Further, the characteristics of the desired fluid flow within a tube often dictate varying the internal diameter along the length of the tube while keeping its outer diameter constant. It may be desired to have a particular cross-section at one location along the tube, for example, to give a particular flow velocity or to promote or eliminate turbulence, and a different cross-section at another location, for example, to minimize frictional losses.

In addition, it may be desired to vary the thickness of a tube along its length to present paths of different length for the conduction of heat laterally through the tube in order to give a desired temperature distribution along either the interior or the exterior of the tube.

It still further may be desired to vary the thickness of a tube along its length so that the tube can be later severed at locations therealong to produce several tube sections of different thicknesses, each section being of either uniform or non-uniform thickness, so that each section need not be extruded separately.

It will be apparent that a tube may be of varying wall thickness for a combination of the foregoing exemplary reasons, or for a number of reasons not mentioned but which would be known to one having ordinary skill in the art. Tubes of varying wall thickness can of course be formed by processes involving casting, forging, machining and the like. As these processes require relatively large amounts of precision, time, effort, and expense, however, it is far more desirable to produce such tubes by extrusion. It will be noted that where a tube wall thickness varies instead of being constant at the maximum thickness required, a given extrusion press is capable of producing longer extrusions.

Metal tubes of varying wall thickness have been formed by extrusion processes wherein the extrusion ram moves a mandrel of varying cross-section together with the ram through a die, for example, as described in the abovementioned application by Cullen and Merrill. In such processes, however, there is no provision for independently controlling the position of the mandrel relative to the die during extrusion, as for example, by withdrawing the mandrel, so that a particular mandrel can be used to form only one particular type of tube. Consequently a new mandrel must be designed, made, and installed in the extrusion press each time a tube of wall thickness varying in a different manner is to be extruded.

Metal tubes of varying wall thickness also have been formed by extrusion processes wherein a mandrel of varying cross-section is advanced, independently of the ram, forwardly with respect to the die; see, for example, US. Patent 1,854,411 to Leighton. Such processes, however, sufier from the inherent limitation that the wall thickness of an extruded tube must either increase or decrease along its length-it cannot increase and then decrease, or decrease and then increase. Further, this limitation applies not only to the processes, but also is reflected in the apparatus heretobefore used for carrying out such processes. For reasons which will be made apparent by the following description of the invention, these apparatuses did not provide means sufiiciently powerful to be capable of retracting the mandrel with respect to the die at any time during extruding.

This invention advantageously provides flexible methods and apparatus for conveniently extruding elongate metal members having wall thicknesses which vary in any desired pr'e-determined manner.

For a better understanding of the invention, and of its other details, objects, and advantages, reference is now made to the accompanying drawings, which show, for purposes of illustration only, a preferred embodiment of the invention. In the drawings:

FIGURES 1-4 are semi-diagrammatic sectional plan views of an extrusion press which represents the apparatus of the invention upon which the process of the invention can be carried out, in the fully retracted, billet crushing, billet piercing, and extruding positions, respectively.

FIGURE 5 is a semi-diagrammatic sectional plan view of a stepped mandrel extruding a relatively thick-walled tube in accordance with the invention,

FIG. 6 is a semi-diagrammatic sectional plan view of the same stepped mandrel extruding a relatively thinwalled tube in accordance with the invention, and

FIG. 7 is a semi-diagrammatic sectional plan view of a tapered mandrel extruding a tube in accordance with the invention.

The apparatus The extrusion press, which is shown in FIGURES 1-4, consists of four basic assemblies: stationary assembly 100, ram assembly 200, piercer-mandrel assembly 300, and container assembly 400. In the described example, the press is mounted horizontally, and movement during operation is brought about by the introduction or release of a pressurized hydraulic fluid, such as oil. Conventional variable volume, eccentric, oilgear pumps supply the fiuid. Appropriate seals and bearing surfaces are provided where necessary to protect the integrity of the hydraulic system. For the purposes of this description, all valves are three-way valves connected to a line leading to a pressure chamber within the press for closing it, opening it to a pump, or venting it to a reservoir. Suitable metering valves are provided.

In the stationary assembly 100, which is connected to a foundation, front platen 102 supports die backup 104 which in turn carries at its front end a hard steel die 105 having a throat 106. A plurality of tie-rods 107 are rigidly secured at their ends to front platen 102 and ram cylinder 108, fixing them in a spaced relation. Ram cylinder 108 forms ram chamber 110 and a plurality of pullback chambers 114. Ram chamber 110 communicates through its rearward wall with a hydraulic line 112, while pullback chambers 114 communicate through their rearward walls with hydraulic lines 116 and through their forward walls with hydraulic lines 122 having valves 123. Lines 112 and 116 are connected in parallel to a common line 118 having valve 120 therein, and lines 122 may also be connected to a common line. The rear of ram cylinder 108 is shaped to form a mandrel retraction piston 124. A bore 125 extends axially through piston 124, opening into the ram chamber 110. (The term main ram is another art recognized term having the same meaning as the term ram used herein.)

The ram assembly 200 is mounted on rails or other suitable means (not shown) for movement relative to stationary assembly 100 in such a manner that its rearward portion forms a piston closely fitting within ram chamber 110. The main body of the ram 202 includes stem 204, crosshead 206, piercer piston chamber 210, and axial bore 211 extends completely therethrough. Piercer piston chamber 210 communicates through its forward wall with flexible hydraulic line 212 having valve 214, and through its rearward wall with flexible hydraulic line 216 having valve 218. A plurality of pullback rods 220 secured to the crosshead 206 extend rearwardly through bores 126 in ram cylinder 108, being connected at their ends to pull-back pistons 222 closely fitting within pullback chambers 114.

The piercer-mandrel assembly 300 includes a mandrel 302 mounted for movement within bore 211 in ram 202 and bore 124 in ram cylinder 108. (The term piercer ram is another art-recognized term having the same meaning as the term piercer-mandrel assembly used herein.) At the front of mandrel 302 is a tip 304 having a piercer 306. The mandrel 302 actually may consist of several components, such as a mandrel (the front portion having the tip and piercer) and a mandrel extension extending rearwardly thereof. The mandrel tip 304 may be either stepped tip 304A or tapered tip 304B. See FIGS. and 6, and 7, respectively. Stepped mandrel tip 304A comprises, from front to rear with exemplary dimensions, piercer 306, cylindrical portion 308 having a diameter of 3.876 inches and a length of inch, conical portion 310 having a length of inch and a taper of between 2 degrees and 8 degrees, e.g., 4 degrees, large cylindrical portion 312 having a diameter of 3.941 inches and a length of inch, abrupt conical portion 314 having a length of inch and a taper of 20 degrees, and a cylindrical base portion 316 having a diameter of 4.250 inches. Tapered mandrel tip 304B comprises, from front to rear with exemplary dimensions, piercer 306, cylindrical portion 316 having a diameter of 7.462 inches and a length of /2 inch, conical portion 318 having a length of 2 inches and a taper of between 2 degrees and 8 degrees, e.g., 4 degrees, cylindrical portion 320 having a diameter of 7.842 inches and a length of inch, an abrupt conical portion 322 having a length of inch and a taper of 30 degrees, and a cylindrical base portion 324 having a diameter of 8.245 inches. (The particular examples of mandrel tips 304A and 340B were of course designed for use with particular dies of different dimensions.) As a further alternative, the mandrel may comprise, from front to rear, a terminal large cylindrical portion, a tapering portion of decreasing cross-section, a small cylindrical portion, a tapering portion of increasing cross-section, and a rearward large cylindrical portion, so that movement of the mandrel tip relative to the die throat during extrusion will result in a tube of varying wall thickness by virtue of its having a constant inner dimension and a varying outer dimension; see the above-mentioned application by Cullen and Merrill. (The term cylindrica as used above will be understood to mean substantially cylindrical, since these surfaces must have a very slight degree of taper to facilitate flow of the metal thereover.) Piercer piston 350 is secured to the mandrel 302 to closely fit within piercer piston chamber 210. After passing through bore 125, mandrel 302 fits slideably into movable stop 352. The front end of movable stop 352 forms a cylinder 353 mating with mandrel retraction piston 124 and forming a mandrel retraction chamber 354 communicating through its rearward end with hydraulic line 356 having valve 358. The rear end of movable stop 352 terminates in a stop surface 360. Stop nut 362 is mounted to move on threads 364 at the rearward end of mandrel 302 and abuts stop surface 360.

In the container assembly 400, electrically heated container 402 is mounted in container carriage 404. The container 402 can be moved rearwardly and away from platen 102, die holder 104, and die 105, by suitable hydraulic means (not shown).

A discussion of certain details of extrusion presses and their operation with which this invention is not immediately concerned appears in the book by Pearson and Perkins entitled The Extrusion of Metals and published in 1961 by John Wiley and Sons, Inc., New York, at pages 74-141.

Extruding a tube of constant wall thickness The operation of the press during the extrusion of a metal tube of constant wall thickness will now be described. With the ram assembly 200 and the piercermandrel assembly 300 in the fully retracted position, as shown in FIG. 1, a preheated, solid, cylindrical, aluminum or aluminum alloy billet 20 and a hollow steel dummy block 22 are elevated by a loading mechanism (not shown) to a position aligned with the mandrel 302 and the cavity in the electrically heated container 402. With valves 123 vented, valve 120 is opened to apply pressure to chambers 114 and through lines 116 and 118, moving ram 202 and pistons 222, and hence the ram assembly 200, forward. Since valves 214 and 218 are vented, either the friction between the mandrel 302 and the ram bore 211 or the action of the piercer piston chamber 210 on the piercer piston 350 carries the piercer-mandrel assembly 300 forward with the ram assembly 200. As the ram assembly 200 continues forward, the stem 204 contacts the dummy block 22 and pushes the dummy block 22 together with the billet 20 into the container 402. The loading mechanism is then withdrawn. When the stem 204 has advanced sufiiciently far to crush the billet 20, valves 120 and 123 are closed, stopping the ram assembly 200 and hydraulically locking it in place to prevent its subsequent rearward movement. At this stage the piercer 306 has not yet contacted the billet, but remains within the ram stem 204. See FIG. 2.

Now, with valve 214 vented to reduce back pressure, valve 218 is opened to apply pressure through line 216 to the rear of piston 350, moving the piercer-mandrel assembly 300 forward until the pointed piercer 306 has penetrated completely through the billet 20, removing a solid portion of metal from its center. At this point the stop nut 362, which has been previously set at a predetermined location on threads 364 at the rear end of mandrel 302, contacts the stop surface 360 to stop the mandrel tip 304 at a position relative to the die throat 106 where the portion of desired cross-section of the mandrel tip 304 is in the die throat 106. See FIG. 3. For example, to extrude a relatively thick tube, smaller cylindrical portion 308 of steped mandrel tip 304A could be positioned within the die throat 106; alternatively, smaller cylindrical portion 316 or a forward part of conical portion 318 of tapered mandrel tip 304B could be positioned within the die throat 106. See FIGURES 7. Conversely, to extrude a relatively thin tube, larger cylindrical portion 312 of stepped mandrel tip 304A could be positioned within die throat 106; alternatively, larger cylindrical portion 320 or a rearward part of conical portion 318 of tapered mandrel tip 304B could be positioned within the die throat 106.

To begin the actual extrusion of the billet, valve 120 is again opened and valve 123 again vented to apply pressure to chambers 114 and 110 through lines 116 and 118, moving the ram assembly forward. The stem 204 pushes the dummy block 22 forward, compressing the billet. (The purpose of the dummy block 22 is to avoid excessive wear on the stem 204 and to allow the stern 204 to have a smaller diameter, thereby reducing friction with the container 402.) The compressed billet 20 then flows in a solid but plastic condition through the sole means of egress, the annular space between the mandrel tip 304 and the die throat 106, to form the extruded tube 24. See FIG. 4. The outer and inner shapes and dimensions of the tube 24 are determined by the shapes and dimensions of the cross-sections of the die throat 106 and the portion of the mandrel tip 304 positioned within the die throat. It will be clear that although the present example contemplates extruding a tube 24 of circular cross-section, the extruded tube or member may have a cross-section of various other regular and irregular shapes. In this respect, it should be noted that the mandrel 302 may be rotated to assume any desired angular relationship with the die 105.

During the extrusion of the billet 20, the piercermandrel assembly 300 is subjected to varying forces. Initially, while the billet is relatively long, the forward billet drag force of the ram assembly 200 acts on the mandrel 302 because of the relatively large amount of friction between the mandrel 302 and the billet 20; at the same time the metal flowing over the decreasing crosssection of the mandrel tip 304 exerts a fairly constant relatively smaller expulsion force tending to expel the mandrel tip 304 from the die and thereby move the mandrel assembly 300 to the rear. As the extrusion progresses, the billet 20 becomes shorter, the friction between it and the mandrel 302 decreases, the forward force on the mandrel assembly 300 decreases, and consequently the magnitude of the forward force on the mandrel assembly 300 may fall below that of the rearward force which 'would cause the mandrel tip 304 to withdraw from the die throat 106.

In order to prevent this, a pressure differential can be maintained. in chamber 210 across piston 350 by proper manipulation of valves 214 and 218 at least during the latter portion of extrusion wherein a net rearward force would otherwise be exerted on the piercer-mandrel assembly 300. To this end valve 218 may be closed, or

opened to a pump through a relief valve, to hydraulically lock the piston 350 forward with respect to the ram assembly 200 prior to the beginning of extrusion. (Note that the forward movement of the ram 202 during extrusion is independent of the piercer-mandrel assembly 300 and tends to reduce the volume of the chamber to the rear of piston 350 and thereby increases to some degree the forward force on the mandrel assembly 300; if the valve 218 is closed, this will require it to be partially vented as the ram assembly 200 advances; if the valve 218 is opened to a pump through a relief valve, the proper pressure will be maintained automatically.) It will be apparent to one having ordinary skill in the art that the use of relief valves and other well known hydraulic devices will simplify the execution of the operations; for ease of illustration, however, it will be hereafter assumed that the valves are operated manually. The magnitude of the pressure in Chamber 210 at the rear of piston 350 must be suflicient to keep a net forward pressure on the piercer-mandrel system 300, but has no precise upper limit, since the nut 362 abuts stop surface 360 to prevent forward movement of the piercer-mandrel assembly 300.

At the completion of the extrusion, valves 218 and are vented to the reservoir to release the forward force on the piercer-mandrel assembly 300 and to stop the ram assembly 200 and release the pressure thereon. Valve 214 is opened to apply pressure through line 212 to the forward face of piston 350, moving the piston 350 to the rear of chamber 210 so that the piercer 306 is withdrawn into the ram stem 204. The container assembly 400 is then moved rearwardly and away from front platen 102, die holder 104, and die 105, so-that the stem 204 pushes the unextruded portion of the billet 20 and the dummy block 22 from the container 402. The container assembly 404 is then returned forward to the position where the container 402 contacts die holder 104. Valve 123 is opened to apply pressure through line 122 to the forward face of piston 222, thereby moving the ram assembly 200 and the piercer-mandrel assembly 300 to the fully retracted position. See FIG. 1. Valves 214 and 123 are then vented to ready the press for another extrusion.

Extruding tube of varying wall thickness In accordance with the invention, the piercer-mandrel assembly 300 may be either advanced or retracted during extrusion, thereby allowing the desired cross-section of the mandrel tip 304 to be positioned in the die throat 106 at any given point in the extrusion, which in turn allows the extrusion of members of wall thickness varying in any particular predetermined manner. The invention contemplates achieving the foregoing by at least two alternative methods.

First method If the mandrel 302 is to be advanced during extrusion, prior to loading the billet 20 and the dummy block 22 into the container 402, the stop nut 362 is rotated by suitable means (not shown) so as to move it along threads 364 to a position sufficiently to the rear of mandrel 302 that the stop nut 362 will not contact movable stop surface 360 until mandrel tip 304 is.in its forward-most position relative to the die throat 106 desired during the extrusion. (If the mandrel 302 is not to be advanced during extrusion, stop nut 362 may be positioned so that it abutsstop surface 360 before extrusion is begun.)

The first method may be best understood by examining the hypothetical case of extruding a tube of constant wall thickness, where the position of the mandrel tip 304 relative to the die throat 1'06 remains unchanged, with the stop nut 362 riding free of the stop surface 360. In this hypothetical case, valves 214 and 218 are manipulated to vary the pressures on the front and rear faces of piston 350 to maintain the mandrel tip 304 in a constant position relative to the die throat 106. The

immediate effect of such manipulation is to vary the forces acting between ram assembly 200 and piercer-mandrel assembly 300, tending to move one with respect to the other. Since the ram assembly is constantly advancing with respect to the die throat 106, valves 214 and 218 must be manipulated in such a manner that the piston 350 moves to the rear of chamber 210 at the rate at which the ram 202 is advancing. In accomplishing this, the foregoing discussion of the varying net force acting on the piercer-mandrel assembly 300 must be considered.

In general,

P is the hydraulic pressure in line 212 acting on the front face of piston 350,

A is the cross-sectional area of piston 350,

P is the hydraulic pressure in line 216 acting on the rear face of piston 350,

F is the expulsion" force tending to expel the mandrel from the die,

P is the billet drag force, and

p is the pressure differential in chamber 210' across piston 350 required to move the piston 350 rearwardly in the chamber 210 at the same rate at which the ram assembly 200 is advancing. For example, in an extrusion over a mandrel tip 304 shaped so as to develop an expulsion force sufficiently large that it exceeds the billet drag force toward the end of the extrusion, valve 214 would initially be opened to apply pressure through line 212 to the front face of the piston 350 to balance the net forward force (F F on the piercer-mandrel assembly 300 and would gradually be closed and vented as this net force decreases as the ram advances; when the net forward force goes to zero, valve 214 would be completely vented and valve 218 would be opened continuously to increase the pressure through line 216 acting on the rearward face of the piston 350 to balance the net rearward pressure (i.e., negative net forward pressure) on the piercer-mandrel assembly 300.

The actual first method of varying the position of mandrel tip 304 relative to the die throat 106 differs basically from the foregoing hypothetical only in that the valves 214 and 218 are manipulated to apply an additional pressure differential in the chamber 210 across the piston 350 to move the piercer-mandrel assembly 300 in the desired direction.

Thus the relationship becomes where Ap is the additional pressure differential in chamber 210 across piston 350 required to move the piercermandrel assembly 300 relative to the die throat 106 and is positive or negative depending upon whether the piercermandrel assembly 300 is to be advanced or retracted, respectively.

This first method is most suitable when extremely accurate positioning of the mandrel tip 304 relative to the die throat 106 is not required. For example, when stepped mandrel 304A is used, the wall thickness of the extruded tube 24 will be the same if any part of one of the cylindrical portions 308 or 312 is positioned within the die throat 106. In addition, the necessity of carefully manipulating valves 214 and 218 to hydraulically stop the mandrel tip 304 in its forwardmost position relative to the die throat 106 can be eliminated by adjusting stop nut 362 so that it will contact stop surface 360 at this position.

This first method may be performed without moving the movable stop 352 relative to the mandrel retraction piston 124; moreover, the disclosed extrusion press apparatus could perform this first method even if ram cylinder 108, mandrel retraction piston 124, and movable stop 352 were fused together to form a single, integral member.

Second method If the mandrel 302 is to be advanced during extrusion, prior to loading the billet 20 and dummy block 22 into the container 402 the valve 358 is opened to apply pressure through line 356 to mandrel retraction chamber 354 so as to retract the movable stop 352 a distance which is at least as great (and preferably equal to) the distance the mandrel tip 304 is to be advanced during the extrusion. When this position is reached, the valve 358 is vented and then closed to hydraulically lock the movable stop 352 thereat. The procedure is then essentially the same as that described above for Extruding a Tube of Constant Wall Thickness, with the superimposed modification that valve 358 is manipulated to change the position of the movable stop 352 relative to the mandrel retraction piston 124 at any time during extrusion. Since the stop nut 362 always contacts the stop surface 360 during this method of extrusion, this modification has the immediate effect of varying the position of the mandrel tip 304 with respect to the die throat 106. In this manner, the position of the mandrel tip 304 having the desired crosssection can always be positioned in the die throat 106. Since the position of the mandrel tip 304 relative to the die throat 106 is independent of the ram assembly 200 and dependent only upon the relative positions of movable stop 352 and mandrel retraction piston 124, simple indicator and control means (not shown) can be provided to accurately determine and regulate it.

While present preferred embodiments of the invention have been illustrated and described, it will be understood that the invention may be otherwise variously embodied and practiced within the scope of the following claims.

We claim:

1. In the operation of an extrusion press having in axial alignment a die, a container adapted to sealably close with said die, a ram adapted to move axially toward said die and into said container, and a mandrel of non-uniform cross-section mounted to move axially within said ram, the method of extruding a metal tube having a wall which is relatively thin at a location along its length between spaced locations at which said wall is relatively thick, which method comprises:

(A) placing an extrudable metal billet in said container,

(B) introducing said mandrel into said die to form an annular extrusion opening,

(C) compressing said billet by hydraulically moving said ram into said container and toward said die, thereby extruding said billet through said opening,

(D) while continuing to so move said ram and extrude said billet, hydraulically moving said mandrel axially in a first direction which disposes a portion of said mandrel of larger cross-section into said die and consequently decreases the cross-section of said opening, thereby decreasing the wall thickness of the resulting extruded tube, and

(E) thereafter, while still containing to so move said ram and extrude said billet, hydraulically moving said mandrel axially in a second direction opposite to said first direction, thereby disposing a portion of said mandrel of smaller cross-section in said die, increasing the cross-section of said opening, and increasing the wall thickness of the resulting extruded tube.

2. The method according to claim 1 wherein said movement in said second direction is achieved by varying hydraulic pressure acting between said mandrel and said ram, causing said mandrel to retract within said ram.

3. The method according to claim 1 wherein said movement in said second direction is achieved by varying hydraulic pressure acting between said mandrel and a member which is fixed relative to said die.

4. The method according to claim 2 wherein said pressure acts between the exterior surface of a piston attached to said mandrel and the interior surface of a chamber located within said ram.

5. The method according to claim 3 wherein said pressure acts upon said mandrel through a movable stop abutted by a nut threaded onto said mandrel, and said member fixed relative to said die is secured to a ram cylinder which is spaced by tie rods from a front platen supporting said die.

6. A method of making a plurality of metal tubes each having a wall which is relatively thick at the ends of the tube and relatively thin between said ends, which comprises:

(F) carrying out the method according to claim 1,

(G) during the same continuous extrusion, repeating said method, thereby forming on the resulting extruded tube at least three locations where said Wall is relatively thick, and

(H) severing said resulting extrusion at at least one of said locations of relatively thick wall which is spaced from the ends of said resulting extrusion.

References Cited UNITED STATES PATENTS Leighton 72260 Hilton 72-260 Schweiger 72-265 Krause 72-260 Reichl 72--260 Hoffmann 72--255 FOREIGN PATENTS 2/1962 Great Britain.

RICHARD J. HERBST, Primary Examiner.

K. C. DECKER, Assistant Examiner. 

